The measurement of bulk density of carbon aggregate in the laboratory has been known for many years. This information is used as a guideline for the commercial production of carbon anodes used in the electrolysis of alumina. However, the use of an easy, adaptable method of measuring the bulk density of large commercial quantities of carbon aggregate at a plant site, where the carbon anodes are mass produced, has not existed. Various methods of doing so have been published; two examples are a U.K. patent application, GB No. 2,116,587A, entitled "Production of Carbon Electrodes for Electrolytic Reduction Cells", and a paper entitled "Correlation of Raw Material Properties With Binder Content of HS Soderburg Paste" by L. Castonguay and S. K. Nadkarni. The paper was published in 1984 from a talk given during an American Institute of Mining, Metallurgical and Petroleum Engineers meeting. It was published by the Metallurgical Society, Warrendale, Pa., in a magazine entitled Light Metals. The U.K. patent application teaches a method of producing carbon anodes by establishing a desired green density using a first set formula and adding a binder to fill fractions of the void spaces using a second set formula. The lack of having an onsite measurement apparatus has meant that carbon anodes would vary considerably in desired properties due to the variations of the starting materials, i.e., the coke and the bituminous pitch binder.
From the standpoint of apparatus, several are known but they have been primarily used in the laboratory. U.S. Pat. No. 4,283,148 discloses an apparatus for measuring bulk density of a sample and is assigned to Aluminum Company of America. This apparatus has not been incorporated into the commercial production of carbon anodes since the operation is very labor intensive and requires the test to be run under controlled conditions. A second U.S. Pat. No. 4,133,090, also assigned to Aluminum Company of America, relates to the control of the binder content in carbon anodes. Although this patent relates to the same subject matter, it teaches a method which is different from the present method.
Now an apparatus and method have been invented which provide a quick and accurate way to measure the bulk density of the starting material used in producing carbon anodes.